1. Field of the Invention
It is known to renovate sewers by relining them. The functions of the liner are fourfold namely to provide structural support, to provide a water tight seal (to prevent the infiltration and ex-filtration of liquids and also the ingress of tree roots), to provide chemical and corrosion resistance, and to afford a smooth hydraulic flow contents.
2. Description of the Related Art
It is known to re-line an existing sewer by introducing into the sewer a pipe of lesser diameter than the sewer so that the outer surface of the pipe lies adjacent to the inner surface of the wall of the existing sewer. Pipes of plastics material are particularly suitable for this purpose. They fulfil the above four functions and lengths of such pipe can be readily pushed, or drawn along the sewer. After the pipe has been inserted into the sewer, the annulus between the inner surface of the wall of the existing sewer and the outer surface of the pipe is ordinarily filled with grout in a process known as slip-lining.
A widely practiced method is to use lengths of pipe manufactured from polyethylene which are butt-welded to form a continuous pipeline which is then drawn into the existing sewer. However, although existing pipes for this purpose normally have a certain degree of resilience, this is not sufficient to allow very substantial bending of the pipe simultaneously with generally longitudinal movement. Thus it is necessary to excavate a trench at least at one end of the sewer run, to enable the pipe to be manipulated and fed into the sewer generally parallel to the axis thereof. Depending upon the depth of the sewer, this trench may have to be of such a length as to cause considerable disruption to traffic and other services.
With a view to avoiding this problem, it is also known to use shorter lengths of rigid pipe which can be inserted into the existing sewer via existing man-holes. This requires the shorter lengths of pipe to be joined together and various techniques have been devised for doing this including the use of screw threads and the use of co-operating spigots and sockets. However, in these cases, the thickness of the pipe wall usually has to be increased in order to accommodate the joint and this increases cost.
In my British Patent No. 2 157 797, I have devised a method of providing sewers with a liner which will satisfy the above four requirements which involves feeding a length of a first plastics pipe into the existing sewer via a man-hole shaft, which pipe has a corrugated wall which enables it to be resiliently deformed in order to enable it to pass from the man-hole shaft into the existing sewer. Then a length of a second plastics pipe is fed into the first pipe. The second pipe has a smooth internal surface and provides rigidity to the composite liner formed by the two pipes. Since waterproofing is already provided by the first pipe, the second pipe can be introduced as a succession of short pipe elements which do not need to be joined together.
It is an object of the present invention to provide an alternative method of relining existing sewers which similarly satisfies the above mentioned four requirements and does not require significant trench excavation to allow entry of the materials used for the relining.